The present disclosure relates to an apparatus for measuring impurities on a wafer and a method of measuring impurities on a wafer.
In addition to achieving high integration and miniaturization of a semiconductor device by using a silicon wafer, reducing impurities on the silicon wafer, which drastically deteriorate the semiconductor device, is an important task. Accordingly, analyzing and managing such impurities, especially, metal impurities, are important to manage the quality of a silicon wafer.
According to a related art, a method of measuring metallic impurities on the edge of a silicon wafer includes mounting a wafer in a chamber and introducing hydrofluoric acid vapor into the chamber to remove an oxide layer on an entire surface of the silicon wafer. Then, there is a method of qualitatively and quantitatively analyzing metallic impurities through an inductively coupled plasma mass spectrometer, after immersing the perimeter of the wafer in a solution mixed with hydrogen fluoride, hydrogen peroxide, and hydrochloric acid, and extracting metallic impurities on the perimeter of the wafer while rotating a stage having the wafer mounted.
However, according to a related art, only the edge portion of a silicon wafer needs to be analyzed, but a portion intruding the front and backside surfaces by about 3 mm in addition to the edge of the silicon wafer is analyzed. Accordingly, it is difficult to accurately analyze only the edge portion of the silicon wafer according to the related art.
Moreover, according to a related art, in order to increase a recovery rate of Cu impurity, a mixed solution of hydrofluoric acid, hydrogen peroxide acid and hydrochloric acid is used. However, when hydrochloric acid is used as a recovery solution, because of a material (28Si35Cl) combined with remaining Si on the silicon surface and Cl in hydrochloric acid after an oxide layer on the silicon surface is decomposed, mass interference with 63Cu occurs. Therefore, in inductively coupled plasma mass spectrometry methods, there may be an error in analyzing Cu impurity, which may measure Cu impurity even when there is no Cu impurity.
Additionally, according to a related art, since an oxide layer on an entire wafer surface is removed in order to analyze metallic impurities on the perimeter of the silicon wafer, particles may be easily adsorbed on the front side surface, so that the wafer may not be used as another measurement sample besides a metallic impurity analysis sample.